1. Field of the Invention
The present invention relates to liquid crystal displays and, more particularly, to a technique suitable for use in a transflective liquid crystal display provided with a backlight and a reflection film.
2. Description of the Related Art
Substantially all mobile phones and mobile information terminals are now provided with liquid crystal displays, and recently, many such mobile electronic apparatuses have been provided with transflective liquid crystal displays.
In general, a transflective liquid crystal display includes a reflector provided on the interior or exterior of a pair of transparent substrates for reflecting incident light from outside and also includes a backlight at the back side thereof. The transflective liquid crystal display can be used as a reflective liquid crystal display and as a transmissive liquid crystal display by switching between a reflective mode in which solar light or an external illumination is used as a light source and a transmissive mode in which light from the backlight is used as a light source.
FIG. 5 is a partial sectional view of a conventional transflective liquid crystal display. In a conventional transflective liquid crystal display 100 shown in the drawing, a first substrate 110 and a second substrate 120, which are composed of a transparent material, such as glass, are opposed to each other, and a liquid crystal layer 130 is enclosed therebetween.
An electrode layer 115 and an alignment film 116 are deposited in that order on a surface of the first substrate 110 facing the liquid crystal layer 130. An electrode layer 125 and an alignment film 126 are deposited in that order on a surface of the second substrate 120 facing the liquid crystal layer 130.
A polarizer 118 is provided on another surface of the first substrate 110 opposite to the liquid crystal layer 130 (i.e., the outer surface of the substrate 110), and a reflector 119 having a reflection film 119a composed of a metal is provided on the outer surface thereof such that the reflection film 119a faces the polarizer 118. A polarizer 128 is provided on the outer surface of the second substrate 120. A backlight 105 for transmissive display is provided on the back of the liquid crystal display 100.
The transflective liquid crystal display 100 having the structure described above is used, for example, as a display area of a mobile phone. When there is sufficient external light, the transflective liquid crystal display 100 operates in the reflective mode in which the backlight 105 is off, and in an environment where there is insufficient external light, it operates in the transmissive mode in which the backlight 105 is on.
However, in the transflective liquid crystal display 100, since the reflector 119 is placed on the exterior of the substrate 110, light entering the liquid crystal display 100 from outside must pass through two substrates, 110 and 120, and two polarizers, 118 and 128, before being reflected by the reflector 119. Therefore, the propagation loss of light is increased, and it is not possible to obtain satisfactory brightness when the transflective liquid crystal display 100 is used as a reflective liquid crystal display.
On the other hand, in the transmissive mode in which the liquid crystal display 100 is used as a transmissive liquid crystal display, although the reflector 119 must transmit light from the backlight 105, the thickness of the reflection film 119a is usually set at 1,000 to 1,500 Å in order to increase the reflectance of light. That is, pores are made in the reflection film 119a in order to transmit light.
However, in the method in which light from the backlight 105 is transmitted by providing the pores in the reflection film 119a, if the aperture ratio of the pores of the reflection film 119a is increased, the reflectance of the reflection film 119a is decreased, thereby decreasing brightness in the reflective mode. Therefore, it is not possible to sufficiently increase the aperture ratio, and satisfactorily bright display is not obtained when the backlight 105 is lit.
In order to solve the problems described above, a structure is disclosed, in which a reflector is placed between two substrates constituting a liquid crystal display so that the number of layers of substrates and polarizers through which light passes before reaching the reflector is decreased, and, by suppressing the propagation loss of light in the reflective mode, brighter reflective display can be obtained. By using such a structure, since display brightness in the reflective mode is ensured where possible, it is believed that brightness in the transmissive mode can be increased by decreasing the thickness of the reflection film for reflecting light to approximately 300 Å, but brightness in the reflective mode is slightly sacrificed.
However, even if such a structure is used, although the display brightness in the transmissive mode is improved, the brightness in the reflective mode is the same as that of the liquid crystal display 100. If the thickness of the reflection film is increased to a certain degree by giving a high priority to the brightness in the reflective mode, the brightness in the transmissive mode becomes insufficient.
As described above, a transflective liquid crystal display in which satisfactorily bright, easily visible display is performed both in the reflective mode and in the transmissive mode has not yet been produced.